This research project undertakes to study the interaction with DNA of three carcinogenic compounds selected for their different modes of action: viz., sulfur mustard, an alkylating agent that can form cross- links in DNA; 9,10-dimethyl 1,2-benzanthracene (DMBA), a polycyclic hydrocarbon which is non-alkylating but which can form cross-links in DNA; and finally, 4-nitroquinoline-1-oxide (4-NQO) which is reported neither to alkylate nor to form cross-links in DNA. Their interaction will be studied in vivo in the naturally synchronous myxomycete, Physarum polycephalum, whose three kinds of DNA can be studied separately by differential timing of incorporation of label during the cell cycle and separated physically by CsCl density gradient centrifugation. The study will determine the degree of binding of each carcinogen to DNA, its effect on cellular mitosis, the nature and the extent of the cellular repair of the lesions induced in DNA by carcinogens as compared to damage inflicted by U.V. and X-irradiation, as well as the effect of inhibitors on such repair processes. The in vitro study of the interaction will take advantage of the Bacillus subtilis transformation system which permits direct exposure of DNA to the ultimately-reactive forms of such carcinogens. The treated DNA will be assayed for loss of biological activity, the induction of mutations, cross-linking effects, genetic and physical evidence of repair processes, and the ability of cell extracts to specifically recognize carcinogen residues bound to DNA and to introduce single strands breaks in proximity to such lesions.